Most conventional drinking straws have a single slender, tubular shape. Such a straw used for sucking drinking water or the like requires a fixed length for suction in view of the depth of the container which is used, while a straw as short as possible is desirable for the storage thereof, carriage, transportation and sale together with a container for beverage onto which such straw is attached.
Double telescopic sucking tubes or drinking straws have been known for solving the above problems. That type of drinking straw or sucking tube consists of a tube section having a larger diameter and another tube section having a smaller diameter which has been inserted into the inside of said larger diameter tube section (hereinafter referred to simply as "larger tube"). In case of sucking use as a drinking straw, the samller diameter tube section (hereinafter referred to simply as "smaller tube") may be drawn out from the larger tube to extend the length of the tube, while the smaller tube may be inserted deeply in the larger tube in the case where such telescopic sucking tube is not extended for suction.
Furthermore, it is desirble in such a double drinking straw or sucking tube that slip-preventing force acts between the smaller and larger tube in order that the smaller tube does not slip out or separate easily from larger tube in the case when the tube is extended for suction. It is also desirable that air not be aspirated from and liquid does not leak from the joint portion between the tubes when in use for suction. In this respect, both the tubes asre arranged in such manner that one end of the smaller tube which remains in the larger tube in the case when both the tubes are used together for sucking a drink is expanded to form a trumpet shape. A convex edge portion of the trumpet-shaped tube is in tight contact with the inner surface of the larger tube.
In the telescoped drinking draw or double sucking tube described above, the smaller tube has one end formed into an annular convex portion such as a trumpet-shaped or knot-like convex portion, and the convex portion is tightly contacted with the inner surface of the larger tube. In the above construction, however, no other portion of the smaller tube comes in tight contact with the inner surface of the larger tube, so that the smaller tube is unstable with respect to the larger tube. As a result, a stable sliding operation as well as a tightly contacting state established between said larger and smaller tubes cannot be maintained.